There are some deposits of nitrates and phosphates in earth's crust. Nitrates are more soluble in water. Nitrates are difficult to reduce under the laboratory conditions but microbes do it easily. Ammonia forms large number of complexes with transition metal ions. Hybridisation easily explains the case of sigma donation capability of NH3 and PH3. Phosphine is a flammable gas and is prepared from white phosphorus.
Which phosphorous on reaction with NaOH gives PH3 as one of the product. This is a